1. Field of the Invention
This invention relates to an arrangement of components for an engine, and particularly to an arrangement of an air intake system, an exhaust system and a cooling system for an engine.
2. Description of Related Art
There are various kinds of arrangements for an engine in disposing its air intake system and an exhaust system. One of the most typical arrangements is a cross-flow type in which the air intake system and the exhaust system are disposed on the opposite sides of the engine relative to each other. Another arrangement, which is not so typical but is well known, is a counter-flow type in which, unlike the cross-flow type, the air intake system and the exhaust system are disposed on the same side of the engine.
One advantage of the counter-flow type is that an intake air charge is easily warmed up by the heat of the burnt charge or exhaust gasses because the air intake passage is positioned in proximity to the exhaust passage. This is advantageous to expedite engine warm up particularly under a cold condition.
Another advantage of the counter-flow type is that there is room on the counter side where neither intake nor exhaust system exists and other engine components can be disposed on this side. Otherwise, this side of the engine can be placed in close proximity to an inner wall of an engine compartment or a protective cowling, if it is incorporated in an outboard motor.
The engine comprises a cylinder body defining a cylinder bore or cylinder bores in which a piston or pistons reciprocate and a cylinder head affixed on an end of the cylinder body. The cylinder head define a combustion chamber or combustion chambers with the piston(s) and the cylinder bore(s). Generally, part of the air intake system and the exhaust system are disposed in the cylinder head. Because both of the systems are positioned on the same side of the engine in the counter-flow type as described above, these systems occupy a relatively large space. This causes the engine to be large.
It is, therefore, an object of the present invention to provide an engine employing the counter-flow arrangement as compact as possible.
On the other hand, the engine usually includes a cooling system arranged to cool the cylinder body and the cylinder head. The cylinder head constitutes a large part of the combustion chamber, and consequently it requires to be cooled more than the cylinder body. In addition, although the counter-flow arrangement is advantageous to expedite warming up of the air intake system, the high-temperature exhaust gasses passing through the passages of the exhaust system conversely tend to overheat the passages of the air intake system under a steady running condition. The air charges passing through the air intake system are hence overheated and the charging efficiency of the engine is deteriorated accordingly.
Additionally, if the cylinder body is overheated, abnormal combustion such as, for example, a knocking phenomenon, is likely to occur. If the cylinder body is overcooled, however, the viscosity of lubricant is increased and thus may prevent the piston from reciprocating smoothly.
It is, therefore, another object of the present invention to provide an engine that has a cooling system that sufficiently cools the cylinder head, including the intake passage formed therein, without overcooling the cylinder body.
Where the cylinder body has a plurality of cylinder bores and both of the air intake and exhaust system have a plurality of passages, it is advantageous for compactness of the engine to dispose one or more intake passages between the exhaust passages. In this arrangement, however, two groups of intake passages with different warm up characteristics result. One group of the intake passages is heated up by the exhaust passages, while the other group is not so warmed. The former group of the intake passages thus is hotter than the latter group. This imbalance of temperature between the intake passages tends to cause an imbalance between the outputs of the cylinders. As a result, the engine""s performance can be adversely affected.
It is, therefore, a further object of the present invention to provide an engine having a cooling system that cools an air intake passage(s) disposed between exhaust passages more than the other intake passages that are positioned outside the exhaust passages.
In accordance with one aspect of the present invention, an internal combustion engine comprises a cylinder body defining a plurality of cylinder bores in which pistons reciprocate. A cylinder head is affixed to an end of the cylinder body and defines combustion chambers with the pistons and the cylinder bores. A plurality of air intake passages are provided for supplying air charges to the combustion chambers. The air intake passages includes inner sections defined within the cylinder head and outside sections disposed outside of the cylinder head. A plurality of exhaust passages are provided for discharging burnt charges from the combustion chambers. An exhaust manifold is provided for collecting the burnt charges from the exhaust passages. The exhaust manifold extends generally along the cylinder body and has an end portion in a direction of its extending axis. At least one of the outside sections of the air intake passages has a passage portion that is positioned adjacent to the end portion of the exhaust manifold. The passage portion overlaps with the exhaust manifold. In a preferred configuration, the passage portion overlaps the exhaust manifold in a view along the extending axis (e.g., a portion of the passage portion is disposed directly above a portion of the exhaust manifold). This engine layout provides a compact configuration.
In accordance with another aspect of the present invention, an internal combustion engine comprises a cylinder body defining at least one cylinder bore in which a piston reciprocates. A cylinder head is affixed to an end of the cylinder body and defines at least one combustion chamber with the piston and the cylinder bores. An air intake passage is provided for supplying an air charge to the combustion chamber. The air intake passage includes an inner section defined within the cylinder head. A cooling system is provided for supplying coolant at least to the cylinder body and to the cylinder head. The cooling system includes a first coolant passage disposed at least within the cylinder body and a second coolant passage disposed in proximity to the inner section of the air intake passage within the cylinder head. A coolant flow control mechanism is arranged to permit the coolant flowing through both of the first and second coolant passages. The coolant flow control mechanism prevents only the coolant within the first coolant passage from flowing therethrough when temperature of the coolant is lower than a preset temperature.
In accordance with a further aspect of the present invention, an internal combustion engine comprises a cylinder body defining a plurality of cylinder bores in which pistons reciprocate. A cylinder head is affixed to an end of the cylinder body and defines combustion chambers with the pistons and the cylinder bores. A plurality of air intake passages are provided for supplying air charges to the combustion chambers. The air intake passages include inner sections defined within the cylinder head and outside sections disposed outside of the cylinder head. A plurality of exhaust passages are provided for discharging burnt charges from the combustion chambers. A cooling system is provided for supplying coolant at least to the cylinder body and to the cylinder head. The cooling system includes a first coolant passage disposed at least within the cylinder body and a second coolant passage disposed in proximity to the inner sections of the air intake passages within the cylinder head. At least one of the intake passages is disposed between the exhaust passages. The second coolant passage is positioned closer to the intake passage, which is disposed between the exhaust passages, than to the other intake passages which are not disposed between the exhaust passages.
For purposes of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
Further aspects, features and advantages of this invention will become apparent from the detailed description of the preferred embodiment which follows.